The invention relates to a method for processing a compressed video stream formed of a sequence of compressed data packets, a computer program and a processing unit for processing a compressed video stream.
The basic idea of change detection is to detect any change of video content caused by, e.g. moving objects or illumination changes. Change detection may be the first step in a video processing chain and can be used to trigger subsequent analysis modules, like object detection, tracking or segmentation.
Usually, change detection is conducted in the so-called pixel domain. That means that the actual pixel data is required for any analysis of a scene of the video stream. As most review data is usually stored or transferred in a compressed representation, the received encoded bit stream has to be completely decoded beforehand in such a scenario. However, the decoding process often has a higher complexity than the analysis algorithm itself.
Therefore, attempts have been made to eliminate the cost-intensive step of decoding to be able to perform change detection analysis directly in the so-called compressed domain. Nevertheless, they still need prior decoding steps. Although they do not demand decoding up to the pixel domain, at least an entropy encoding has to be reverted to access the specific syntax elements of the particular codec. Entropy decoding is usually the most cost-intensive decoding step.